Project Summary/ Abstract Congenital heart disease (CHD) is one of the leading causes of infant mortality and morbidity affecting 8 out of every 1000 newborns in the US. Despite this massive health impact, the genetic causes of this disease are not well understood. In order to better understand CHD, we, along with other labs, are analyzing the genomics of CHD patients. In particular, we examined heterotaxy, a disorder of left-right (LR) patterning that can lead to severe form of cardiac malformation due to failure of cardiac looping. From this genetic approach, we identified RAPGEF5 as a novel candidate gene for heterotaxy and congenital heart disease, which encodes a guanine nucleotide exchange factor that activates RAP GTPase(s). We then modeled this cardiovascular disease in Xenopus by depleting Rapgef5, which recapitulated the human heterotaxy phenotype and demonstrated that rapgef5 affects cardiac looping via regulating the nuclear entry of ?-catenin in Wnt signaling. The main goal of this proposal is to investigate the molecular mechanism by which rapgef5 controls the nuclear localization of ?-catenin. Of note, the mechanism of ?-catenin nuclear translocation remains an outstanding question in Wnt signaling, that has implications for developmental biology and cancer. In this proposal, I have two specific aims based on the following hypothesis: Hypothesis: Rapgef5 maintains nuclear Rap protein(s) in an active GTP bound state, which will preferentially import ?-catenin into the nucleus Aim 1: Kinetic analysis of ?-catenin nucleocytoplasmic shuttling in vitro Aim 2: Identify a RAP GTPase that mediates the ?-catenin nuclear transport system Altogether, these experiments will improve our understanding of cardiac development and the role of rapgef5 in the pathogenesis of CHD as well as its role in Wnt signaling. In the future, this will benefit genetic testing and counseling, as well as improve outcomes in CHD because treatments can be tailored to genotype rather than solely on CHD phenotype. In addition, this application details the my training plan including research mentorship, advanced coursework, training in new techniques, and the development of skills in scientific professionalism, writing, and presentation of data. The research and training outlined in this application will prepare me to pursue a career performing patient-driven research as an independent physician-scientist.